Magnesium has three naturally occurring isotopes with masses of 23.99, 24.99, and 25.98 amu and natural abundances of 78.99%, 10.00%, and 11.01%. Calculate the atomic mass of magnesium.

24.309

Explanation:

Let A, B, and C represent the three isotopes.

For isotope A:

Mass number = 23.99

Abundance = 78.99%

For isotope B:

Mass number = 24.99

Abundance = 10.00%

For isotope C:

Mass number = 25.98

Abundance = 11.01%

Atomic mass of Mg = ?

Atomic mass = [ (Mass of AxA%) / 100] + [ (Mass of BxB%) / 100] + [ (Mass of CxC%) / 100]

Atomic Mass = [ (23.99x78.99) / 100] + [ (24.99x 10) / 100] + [ (25.98x11.01) / 100]

Atomic number = 18.950 + 2.499 + 2.860

Atomic mass of Mg = 24.309